The effect of compressive force with hydroxyapatite block on MC3T3-E1 cells

The impact of mechanical stress on the differentiation and functional expression of osteoblasts is not yet fully understood. The present study sought to clarify the effects of mechanical stress as represented by the compressive force of a hydroxyapatite (Hap) block on osteoblast-like cells (MC3T3-E1). The experimental groups consisted of two groups. The first was a UH group in which MC3T3-E1 cells were incubated in a polystyrene dish. A Hap block was fixed on the cells, and compressive force was applied (Group A). The second was an OH group in which MC3T3-E1 cells were incubated on a Hap block that was fixed on the dish and then inverted, and compressive force was applied (Group B). The control group used a standard culture of MC3T3-E1 cells grown on a dish (C group). In each experimental group, the compressive force was applied after cells reached confluence. On incubation days 1, 2, and 3, total protein levels were measured and real-time polymerase chain reaction assays were performed to determine mRNA expression of alkaline phosphatase (ALP), osteocalcin (Oc), receptor activator of nuclear factor kappa-B ligand (RANKL), and osteoprotegerin (OPG). Total protein levels increased over time in both the UH and OH groups, but were significantly lower than in the C group. This suggests that compression inhibited cell growth. Oc and ALP levels increased over time in the UH group, but Oc after 3 days of compression and ALP at each time point were both significantly lower than in the C group. RANKL in the UH group also increased over time and was significantly higher than in the C group, but OPG was significantly lower. These findings suggest that the compressive force may have inhibited osteoblast differentiation and enhanced osteoclast differentiation. Meanwhile, Oc and ALP increased over time in the OH group, and Oc at Day 3 and ALP at each time point were both significantly higher than in the C group. Conversely, RANKL decreased over time and was significantly lower than in the C group. These findings suggest that, unlike in the UH group, compressive force may have enhanced osteoblast differentiation and inhibited osteoclast differentiation. Taken together, these findings suggest that compressive force applied to MC3T3-E1 cells using a Hap block may inhibit cell growth, and that the direction of force application may affect osteogenic functional expression and osteoclast differentiation.